(1) Field of the Invention
The present invention relates to a radar apparatus, a method for controlling the same, and a vehicle including the same, and more particularly to a radar apparatus that transmits a multiplicity of carrier waves having different directional characteristics, and detects an object.
(2) Description of the Related Art
Vehicles have been equipped with on-vehicle radar apparatuses for preventing collision with other vehicles and detection of obstacles. The on-vehicle radar apparatuses have different detection ranges (detection distances and directions) depending on statuses of the vehicles. For example, while traveling, the on-vehicle radar apparatuses detect an obstacle approximately 100 meters forward. Furthermore, when the vehicles are backing up, the on-vehicle radar apparatuses detect an obstacle in a wider area approximately 10 meters backward of the vehicles.
Furthermore, when the vehicles are traveling, the on-vehicle radar apparatuses need to detect obstacles at different distances and in different directions, depending on a traveling direction of the vehicles. For example, the on-vehicle radar apparatuses need to detect obstacles at a long distance in a straightforward direction. In the case of diagonally forward of the vehicles, the on-vehicle radar apparatuses need to detect not obstacles at a long distance, but obstacles in a wider area with respect to the vehicles.
For such requirements, for example, Japanese Unexamined Patent Application Publication No. 10-27299 (referred to hereinafter as Patent Reference 1) discloses an on-vehicle radar apparatus that emits, straight forward of a vehicle, a beam having a narrower width and that emits, in a diagonally forward direction closer to a side of the vehicle, a beam having a wider width.
FIG. 1 illustrates a block diagram of a conventional on-vehicle radar apparatus described in Patent Reference 1. A radar apparatus 100 illustrated in FIG. 1 includes a distance and speed detecting unit 101, a signal processing unit 102, and a switched mode multi-beam antenna 103.
The multi-beam antenna 103 includes antennas 104, 105, and 106, and a switch 107.
The antenna 104 emits a beam 111 diagonally forward left of a vehicle equipped with the radar apparatus 100. The antenna 105 emits a beam 110 forward of the vehicle. The antenna 106 emits a beam 112 diagonally forward right of the vehicle.
The beam 110 detects an obstacle at a long distance, and has a narrower beam width. The beams 111 and 112 detect an obstacle at a short distance, and have a wider beam width.
The switch 107 switches between the antennas 104, 105, and 106 for emitting a beam.
When the beam emitted from one of the antenna 104, 105, and 106 is reflected from an obstacle, the one of the antenna 104, 105, and 106 that has emitted the beam receives the reflected beam.
The signal processing unit 102 performs signal processing, such as analog-digital conversion, on the beam received by the one of the antenna 104, 105, and 106. The distance and speed detecting unit 101 detects, based on a signal obtained through the signal processing by the signal processing unit 102, a distance from the vehicle equipped with the radar apparatus 100 to the obstacle, a relative speed with respect to the obstacle, and other information.
With such a configuration, the conventional radar apparatus 100 can switch between detection ranges by switching between the antennas 104, 105, and 106 using the switch 107.
Furthermore, for example, Japanese Unexamined Patent Application Publication No. 8-262133 (referred to hereinafter as Patent Reference 2) discloses a radar apparatus that switches between radio waves emitted from an antenna in a time-sharing mode. The radar apparatus disclosed in Patent Reference 2 is an FM radar apparatus, and transmits FM signals having a predetermined level, from antennas at different times. The radar apparatus switches between the FM signals using a switch.
However, both of the conventional radar apparatuses disclosed in Patent References 1 and 2 need to select, using a certain switch (for example, an electronic switching device), one of transmission antennas, or the transmission antennas alternately in a time-sharing mode in order to switch between detection distances and detection directions of the vehicle equipped with one of the radar apparatuses. Furthermore, some on-vehicle radar apparatuses use pulses or carrier waves having millimeter or quasi millimeter wave frequencies. In other words, switching devices need to be interposed in transmission paths having a high frequency up to several tens of GHz. Thus, the conventional radar apparatuses need to be controlled without any influence of reflection, loss, and change of waves with the passage of time in such transmission paths. In other words, there is a problem that designing of the conventional radar apparatuses has difficulty due to necessity of switching devices.
In general, a GaAs PIN diode and others are used as such switching devices. Costly switching devices further increase the cost of radar apparatuses. In other words, the conventional radar apparatuses including such switching devices have a problem of increased costs.